The present disclosure relates to image pickup systems, image pickup apparatuses, and programs.
In recent years, use of digital single-lens reflex (SLR) cameras has rapidly become widespread. However, a demand for smaller and lighter camera bodies of digital SLR cameras has not been satisfied. It is considered to be inevitable that the camera body for a digital SLR camera will be large and heavy because such a camera body will include a reflex mirror and a pentaprism. The reflex mirror is used for switching between optical paths for shooting and for a viewfinder. The pentaprism is used for guiding a subject image to an optical view finder (OVF).
Mirrorless digital SLR cameras have been introduced. Such mirrorless cameras have no reflex mirrors because an electronic viewfinder (EVF) is used instead of an OVF, thereby achieving a small and light camera body.
Such mirrorless cameras have no submirrors in addition to having no reflex mirrors. Submirrors are used for guiding incident light to a focus detection unit. As a result, a focus may not be detected by phase-difference detection in camera bodies of mirrorless cameras.
In addition, mirrorless digital SLR cameras have a flange focal length smaller than that of digital SLR cameras. Accordingly, interchangeable lenses that can be mounted on digital SLR cameras may not be used as they are with mirrorless digital SLR cameras. To utilize existing interchangeable lenses, mount adaptors are used. Interchangeable lenses for digital SLR cameras can be mounted on mirrorless digital SLR cameras via mount adaptors.
To enable mounting of interchangeable lenses compatible with phase-difference detection, an image pickup apparatus has been proposed which is used with a mount adaptor provided with a focus detection unit that detects a focus by phase-difference detection (For example, see International Publication No. 2008/099605).
In addition, a camera body for a mirrorless digital SLR camera has been proposed which has an image pickup device with phase-difference detection elements disposed on the image pickup device to achieve more rapid focus detection (For example, see Japanese Patent No. 3592147).